1. Field of Invention
This invention relates to an internal combustion engine of a premixed charge compression self-ignition type, and in particular, an internal combustion engine of a premixed charge compression self-ignition type in which an ignition timing of fuel can be controlled.
2. Description of the Related Art
In recent years, a premixed charge combustion system has been proposed as a combustion system for a diesel engine. In this system, fuel and intake air are premixed with each other by, for example, advancing fuel injection timing to promote making lean and homogeneous mixture to significantly reduce NOx (oxides of nitrogen) and smoke emission.
However, there has been a problem in this premixed charge combustion system that controlling ignition timing of the mixture is difficult. Namely, in conventional combustion system, since ignition begins during injection of fuel, ignition timing is controllable to some extent by controlling fuel injection timing. However, in the premixed charge combustion system, since ignition begins after fuel injection is completed and a premixing period passes, ignition timing is uncontrollable by fuel injection timing.
Inappropriate ignition timing of the mixture may result in deterioration of thermal efficiency (fuel consumption) and exhaust gas emission. For example, if the ignition timing of the mixture is too early (i.e., before a compression top dead center), this may cause an increase of heat loss, and a NOx generation since the mixture is compressed by a piston after its ignition which results in raising temperature in the cylinder.
Therefore, it has been a subject to appropriately control the ignition timing of the mixture in the internal combustion engine in which the premixed charge combustion is executed. For example, it is described in Japanese laid-open Patent Application No. 2001-20784 to control temperature, pressure, characteristic, etc., of the mixture in order to control the ignition timing. However, it is not described in Patent Application No. 2001-20784 how each of controlled systems is controlled in practice.